Field of the Invention
The invention relates to a method of cooling at least one superconductive cable which is arranged in a cryostat having at least one thermally insulated pipe in a free space surrounded by the pipe, wherein the cable and at least one tubular structure are arranged in the free space and through which a cooling agent is conducted to a distal end from a feeding point located at an end.
Such a method is disclosed, for example, in EP 2 200 048 A1.
Description of Related Art
In today's technology, a superconductive cable includes an electrical conductor composed of a composite material which contains ceramic material which at sufficiently low temperatures changes over into the superconductive state. The electrical direct current resistance of an appropriately constructed conductor is zero with sufficient cooling as long as a certain current level is not exceeded. Suitable ceramic materials are, for example, materials doped with rare earths which have become known under the name ReBCO (rare-earth-barium-copper oxide), wherein YBCO (yttrium-barium-copper oxide) are particularly among these materials. Another of these superconductive materials is, for example, BSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures for bringing such a material into the superconductive state are, for example, between 67K and 110K. Suitable cooling agents are, for example, nitrogen, helium, neon and hydrogen or mixtures of these materials.
U.S. Pat. No. 3,800,062 A describes a method for operating a plant with superconductive cables. In the enclosure, for example, three superconductive cables with a pipe shaped core are arranged in a cryostat. A cooling agent supplied from a cooling station is fed into the cryostat at an end thereof and is returned as a heated cooling agent from the distal end of the cryostat through a separate pipe or a second cryostat to the cooling station. The heated cooling agent can additionally be returned with a special pipe system through sections of the tubular cores of the cables which are connected with the use of locks or stops at various locations to the separate pipe or the second cryostat.
A method as it is described above is disclosed by, for example, from EP 2 200 048 A1. This reference shows an arrangement with a superconductive cable which is surrounded by a cryostat for conducting a cooling agent through a free space thereof. The cryostat consists of two concentrically arranged metal pipes between which is arranged a vacuum insulation. Also arranged in the free space of the cryostat is a pipe through which a cooling agent, which has been fed into the cryostat at the near end, can be returned from the distal end of the arrangement. The cooling agent becomes warmer already in the free space of the cryostat during its return from the distal end of the arrangement. Another heating occurs during the return through the pipe with a corresponding return action on the cooling agent introduced into the cryostat at the feeding point. The efficiency of the cooling action is generally negatively influenced as a result.